1. Field of the Invention
The present invention relates to a liquid crystal display device and a method of manufacturing the same
2. Description of the Prior Art
As a display device of an audio-visual (AV) machine and an office automation (OA) machine, a liquid crystal display device (LCD) has been widely used because of its merits including thin thickness, a light weight, a low power consumption, and the like. This LCD includes a pair of substrates which face each other. Moreover, the LCD is configured to seal liquid crystal between the substrates. The LCD is designed to display an image by controlling a direction of alignment of liquid crystal molecules with an electric field using electrodes provided on the substrates, and thereby modulating light irradiated on the LCD. Concerning the LCD as described above, demands for higher definition and an increase in the screen size are growing in recent years, and it is important to enhance uniformity of a gap between the substrates facing each other in order to improve display quality.
Here, a typical method of manufacturing the conventional LCD will be outlined.
Firstly, in terms of a thin film transistor (TFT) substrate in the typical method of manufacturing the conventional LCD, gate lines and gate electrodes are formed with metal, such as aluminum (Al), on a transparent insulative substrate such as a glass substrate. On the gate lines and the gate electrodes, an a-Si layer and an n+a-Si layer are formed into island shapes in a TFT forming region through a gate insulating film made of a silicon nitride film or the like. Next, drain lines and source/drain electrodes are formed with metal such as chromium (Cr), and then channel etching is performed. Thereafter, a passivation film made of a silicon nitride film or the like is deposited, and then a transparent electrode such as indium tin oxide (hereinafter abbreviated as ITO) is deposited thereon to form pixel electrodes. Thereafter, an alignment layer film is coated and subjected to an alignment treatment in a predetermined direction to form the TFT substrate.
Meanwhile, in a counter substrate facing the TFT substrate, color filters in respective colors of RGB are formed on a transparent insulative substrate so as to correspond to the respective pixels. After forming a black matrix in positions corresponding to the TFTs and the lines of the TFT substrate, a transparent electrode made of ITO is formed. Then, an alignment layer is coated thereon and subjected to an alignment treatment in a predetermined direction to form the counter substrate.
Thereafter, as shown in FIG. 4A, a sealing member 105 made of photocuring resin or the like is coated on a line-extracting portion outside a display area of a TFT substrate 102 by use of a dispenser or the like. Then, as shown in FIG. 4B, an appropriate amount of a liquid crystal material 104 is dripped in a region surrounded by the sealing member 105 by use of a liquid crystal dripping dispenser 131 or the like. Then, spacers such as polymer beads or silica beads are sprinkled over a display area of a counter substrate 103. Thereafter, as shown in FIG. 4C, the TFT substrate 102 and the counter substrate 103 are aligned and adhered to each other at predetermined reduced-pressure atmosphere. Subsequently, the inside of a vacuum chamber is restituted to atmospheric pressure, whereby the TFT substrate 102 and the counter substrate 103 are pressed against each other from both outer sides utilizing a pressure difference from the atmospheric pressure. Simultaneously, light such as ultraviolet rays is irradiated onto a backside of the TFT substrate 102 to cure the sealing member 105. Then, the TFT substrate 102 and the counter substrate 103 are cut out at predetermined positions outside the sealing member 105 to finish a LCD 101.
Here, outgoing lines are formed at an outer peripheral portion of the TFT substrate 102 for connecting the gate lines as well as the drain lines to driver chips for driving the LCD 101 as well as to external circuits such as circuit boards. As the sealing member 105 is provided at this portion, a cross section of the region provided with the sealing member causes irregularities which correspond to the thickness of the outgoing lines. If the outgoing lines are arranged at a constant pitch along a certain direction, a change in the gap between the substrates caused by the irregularities attributable to the outgoing lines is not visually detectable. In the LCD, the TFT substrate 102 is connected to the external circuits by use of flexible substrates. Accordingly, the flexible substrates are disposed at given intervals. For this reason, the outgoing lines are also formed at the peripheral portion of the TFT substrate 102 in bent shapes. Therefore, the directions and intervals of the outgoing lines become uneven, and regions having narrow intervals between the outgoing lines and regions having wide intervals between the outgoing lines are generated at a certain interval. Resultantly, such a large cycle of irregularities due to the narrow and wide intervals is reflected in the gap between the substrates and is rendered visually detectable.
This problem will be described with reference to the drawings. FIG. 1A and FIG. 1B are views schematically showing a pattern of outgoing lines on a TFT substrate in a conventional LCD. As shown in the drawings, gate lines 112 and drain lines 116 are arranged at even intervals in a display area. However, outgoing lines 108 are bent at a peripheral portion of the TFT substrate 102 in conformity to pitches of flexible substrates 107 and are thereby formed into a pattern as shown in the enlarged view. As a result, the density of the outgoing lines 108 is high in a region 111 (a region A) where the outgoing lines 108 are arranged obliquely relative to an edge of the TFT substrate 102. Meanwhile, the density of the outgoing lines 108 is low in a region 112 (a region B) where the outgoing lines 108 are orthogonal to the edge of the TFT substrate 102. In addition, the outgoing lines 108 are not formed in a region 113 (a region C) between the adjacent flexible substrates 107. Accordingly, the gap varies in the respective regions depending on the difference in the density of the outgoing lines 108, and such variation of the gap causes deterioration in the display quality.
To suppress the variation of the gap attributable to the outgoing lines as described above, the LCD disclosed in Japanese Unexamined Patent Publication No. 2000-187236 includes a plurality of signal lines which are formed on one of a pair of substrates disposed so as to face each other while interposing a liquid crystal layer therebetween and are extracted to an end of the substrate, an interlayer insulating film formed on the signal lines, and a sealing member formed around the pair of substrates and configured to adhere the pair of substrates to each other while maintaining a given interval. Moreover, there is disclosed a liquid crystal display element in which a dummy member is formed between a signal line below a sealing portion and an adjacent signal line below the sealing portion in the same process, in the same width, and at the same pitch as the signal lines.
However, the structure disclosed in Japanese Unexamined Patent Publication No. 2000-187236 (p. 3 to 4, FIG. 1) has the following problems.
A first problem is that the outgoing lines 108 become denser along with the progress in terms of higher definition and narrower framework of the LCD. As a consequence, it is not possible to suppress unevenness in the gap attributable to the difference in the density of the outgoing lines sufficiently, and the display quality would be eventually deteriorated. Specifically, as described above, the region where the sealing member is provided is divided into the region A having high density of the outgoing lines 108, the region B having low density of the outgoing lines 108, and the region C where outgoing lines 108 are not formed. As an effective height (an average level difference) from a surface of the substrate varies among the respective regions, the difference in level between the region A and the region B is not solved even if the dummy pattern is provided in the region C, and the gap varies along with the difference in level. Moreover, the technique according to Japanese Unexamined Patent Publication No. 2000-187236 merely aims at equalizing the width and the pitch of the dummy pattern to those of the outgoing lines, or aligning the extending direction of the dummy pattern to the direction of the signal line. In other words, the technique according to Japanese Unexamined Patent Publication No. 2000-187236 does not define the width, the pitch, and the like of the dummy pattern so as to correlate with the display quality. Accordingly, this technique cannot maintain the display quality at a certain level. In addition, Japanese Unexamined Patent Publication No. 2000-187236 is only focused on the difference in level in terms of the edges where the gate lines and the drain lines are extracted. As the dummy pattern is not formed on an edge where the outgoing lines are not provided, this technique cannot suppress the variation in the gap between the substrates on the entire LCD.
Meanwhile, a second problem is that the outgoing lines formed on the same layer as the gate lines as well as the outgoing lines formed on the same layer as the drain lines tend to be short-circuited with the dummy pattern because the dummy pattern is formed at the same time in the step of forming the outgoing lines. As a result, defects attributable to short circuits among the lines may occur more frequently.
Meanwhile, a third problem is that there may be a case where it is not possible to cure the sealing member 105 completely. While the sealing member 105 is supposed to be cured by irradiating light such as ultraviolet rays onto the backside of the TFT substrate 102, the technique according to Japanese Unexamined Patent Publication No. 2000-187236 does not set the width, the pitch, and the like of the dummy pattern in consideration of a condition for curing the sealing member 105.
The present invention has been made in consideration of the foregoing problems. A main object of the present invention is to provide a LCD and a manufacturing method thereof, which are capable of improving display quality by achieving a uniform gap in a region provided with a sealing member located in the periphery of a substrate, and capable of preventing defects such as short circuits among outgoing lines or insufficient curing of a sealing member.